1. Field of the Invention
The present invention relates to semiconductor processing method and system for processing a semiconductor chip with high accuracy.
2. Description of the Related Art
Conventionally, in processing and analyzing a semiconductor chip, a processing to a semiconductor chip has been performed from a surface thereof using a focused ion beam (FIB). In recent years, however, as a design rule for a semiconductor process becomes finer and finer and a semiconductor chip includes more and more layers stacked therein, it becomes more difficult to analyze a semiconductor chip from a surface thereof. In such circumstances, techniques for performing processing and analysis of a semiconductor chip from a back surface have become important. To analyze a semiconductor chip from a back surface thereof, a silicon substrate has to be processed so as to have a very small thickness. In general, in order to process a silicon substrate so as to have a small thickness, as shown in FIG. 9, it is necessary to form a trench such that a remaining thickness of silicon is precisely controlled to be uniform. In FIG. 9, the reference numeral 1 denotes a silicon substrate located in the back surface side of a semiconductor device and the reference numeral 4 denotes an interlevel insulation film located in the surface side of the semiconductor device. The interlevel insulation film 4 includes a polysilicon layer, a metal interconnect layer and the like together constituting a semiconductor integrated circuit or the like. The reference numeral 6 denotes a focused ion beam generator used for forming a trench in a silicon substrate. The reference numeral 6a denotes a focused ion beam.
When a trench (large area excavation in silicon) is formed by performing a focused ion beam processing from a back surface of a semiconductor chip, OBIC (optical beam induced current) generated when a PN junction is exposed to light is used in detection of an end point of a trench processing. Specifically, in this method, a laser is irradiated to part of a semiconductor chip which is to be processed, increase in OBIC caused as a silicon film thickness is reduced is monitored, and a maximum point in a graph showing observed variation points is determined to be a processing end point. This processing method will be described with reference to FIG. 10. In FIG. 10, the reference numerals 1 through 5 show a structure of a semiconductor chip. Specifically, the reference numeral 1 denotes a silicon substrate of which a surface is a back surface of a semiconductor chip. The reference numeral 2 denotes a polysilicon layer. The reference numeral 3 denotes a metal interconnect layer. The reference numeral 4 denotes an interlevel insulation film. The reference numeral 5 denotes a separation layer. Moreover, the reference numeral 6 is a focused ion beam generator. The reference numeral 6a is a focused ion beam. The reference numeral 7 denotes a laser light irradiator for irradiating laser light used for observing the progress of formation of a trench. The reference numeral 7a is laser light. In the structure of FIG. 10, the focused ion beam 6a is scanned while part of the semiconductor chip to be processed is exposed to the laser light 7a using the laser light irradiator 7, thereby performing a trench processing. As the trench processing proceeds in such a manner, a silicon remaining thickness becomes smaller and smaller and, accordingly, light irradiated to a PN junction at a silicon interface is increased. The reference numeral 22 denotes a measurement instrument for measuring OBIC varying according to the amount of irradiated light. This variation in OBIC is shown in a graph of FIG. 11. FIG. 11 is a graph showing variation in OBIC relative intensity obtained by the measuring equipment 22 with processing time. In FIG. 11, an OBIC relative intensity is increased as the trench processing proceeds. By monitoring the variation in the OBIC relative intensity and detecting a maximum point of the OBIC, a processing end point is determined. Details of the trench processing technique employing OBIC observation are described in the following non-patent reference 1.
(Non-patent reference 1) J. Vac. Sci. Technol. B20 (6), November/December 2002
(Patent reference 1) Japanese Laid-Open Publication No. 2001-50919